Semiconductor devices capable of controlling large currents have been used for many years in numerous devices and applications such as control of high power generators, power sources and power distribution grid connections, air conditioning and heating installations, electric motor control and power converters for large electrical loads such as battery chargers for electrically powered vehicles. However, many semiconductor devices such as silicon carbide (SiC) MOSFETs have low current ratings as an incident of their manufacturing processes. On the other hand, semiconductor switches having especially high current ratings may command a premium price or present some other performance drawback relative to transistors having lower current ratings. Therefore it is common to construct switching arrangements with a plurality of semiconductor switches having lower current ratings connected in parallel to obtain a high current capability and rating for the overall switching arrangement.
Simplicity and low numbers of electrical and electronic devices are also important to economical manufacture and high power density of such switching arrangements and it is generally preferred to drive the switches in parallel with a single gate driver circuit that applies the same currents and voltages to control electrodes of all of the paralleled switches in common. However, discrete switches will inevitably exhibit some mismatch among such parameters as ON-resistances, causing conduction losses, and threshold voltages, causing switching losses, and suffer higher junction temperatures and shorter reliably usable life.
While this problem with use of a plurality of parallel connected power switches and the need for equalization of performance of parallel-connected power switches has been long-recognized, prior efforts to approach equalization of performance has required separate control circuits for each of the parallel-connected power switches to develop separate drive waveforms for the respective power switches. Further, such known approaches exhibit significant disadvantages and have not provided a complete or robust solution to the problem, even at the cost of substantial complexity and expense. Moreover, known approaches to this problem are generally specific to a particular number of parallel-connected power switches and increase greatly in complexity and cost with increases in the number of power switches connected in parallel.